1. Field of the Invention
The present invention relates to a lens array and an image display apparatus of a projection type, in particular, to a lens array suitably used in a liquid crystal device, in which liquid crystal sealed between a pair of substrates exhibits a twisted orientation between the substrates, and an image display apparatus of a projection type using the lens array.
2. Description of the Related Art
In the projection type image display apparatus, for example, lights comprised of primary colors of red, blue and green are penetrated through respective liquid crystal devices (light valve) and an image component for each of the colors is formed, so that the image components are synthesized to thereby create a desired color image and project the image on a screen, or the like.
FIG. 1 shows a partial schematic illustration of a configuration in cross section of a liquid crystal device 1 of a TN (twisted nematic) mode used as a light valve of an image display apparatus of a projection type. The liquid crystal device 1 is mainly comprised of a TFT substrate 2, a counter substrate 3, liquid crystal 4 and a spacer (not shown). In the TFT substrate 2, pixel electrodes 6 are arrayed in an inner surface of a glass substrate 5 in a matrix shape, a black matrix region 7 is provided in a region surrounding the pixel electrodes 6, and an alignment film 8 made of a polyimide film, or the like, is provided on the pixel electrodes 6 and the black matrix region 7. The pixel electrodes 6 are formed in a window shape by means of a transparent electrode film. The black matrix region 7 is a region where TFTs (thin-film transistor) for turning on/off the respective pixel electrodes 6, wirings such as data lines and scan lines, and the like are provided. The surface of the black matrix region 7 is covered with a black mask made of a metal material such as chrome, resin black, or the like. In the counter substrate 3, transparent counter electrodes 10, such as ITO, and an alignment film 11 made of the polyimide film, or the like, are provided for an entire inner surface of a glass substrate 9. The counter substrate 3 is also provided with a light blocking film 12 formed in a lattice shape in such manner as opposed to the black matrix region 7 of the TFT substrate 2. The light blocking film 12 is a black mask made of a metal material such as chrome, the resin black, or the like.
The TFT substrate 2 and the counter substrate 3 are disposed in such manner as opposed to each other via the spacer. The liquid crystal 4 is sealed into between the alignment film 8 of the TFT substrate 2 and the alignment film 11 of the substrate 3 and held in a sandwiched state therebetween. As the liquid crystal 4 to be sealed thereinto, liquid crystal of the TN mode, which are twist-oriented through 90 degrees between the TFT substrate 2 and the counter substrate 3 by the alignment films 8 and 11, is widely used. In the liquid crystal device 1 configured in the foregoing manner, the respective TFTs are turned on/off by means of an image signal so that the orientation state of the liquid crystal 4 can be controlled between the pixel electrodes 6 and the counter electrodes 10. Therefore, in the liquid crystal device 1 of a transmission type, light entering the liquid crystal device 1 from the counter-substrate-3 side is first converted into a linearly polarized light having a predetermined direction by means of a light-entering-side polarizing plate (not shown), and then enters the liquid crystal 4 from the counter-substrate-3 side. A linearly polarized light transmitting through a region is twisted in polarizing axis and emitted from the TFT-substrate-2 side, while a linearly polarized light transmitting through a different region is not twisted in polarizing axis and emitted from the TFT-substrate-2 side. As a result, one of the linearly polarized light twisted in polarizing axis by the liquid crystal 4 and the linearly polarized light not twisted in polarizing axis by the liquid crystal 4 transmits through a light-emitting-side polarizing plate (not shown). Therefore, the control of the polarizing states per pixel enables predetermined information to be displayed.
FIG. 2 schematically shows an orientation state of the liquid crystal 4 sealed into between the alignment film 8 of the TFT substrate 2 and the alignment film 11 of the counter substrate 3. FIG. 2 is a perspective view from the light-emitting side, in which liquid crystal molecules are in a twist-oriented state by 90 degrees between the TFT substrate 2 and the counter substrate 3. As a method of twisting the liquid crystal 4 by 90 degrees, polyimide films, or the like, constituting the alignment films 8 and 11 are formed on inner surfaces of the respective substrates 2 and 3, and then, a rubbing treatment is performed between the respective alignment films 8 and 11 in directions making 90 degrees with respect to each other, as in respective rubbing directions shown in arrows A1 and A2. Next, the TFT substrate 2 and the counter substrate 3 are attached to each other, between which the liquid crystal 4 is sealed into. As a result, the liquid crystal 4 is oriented with a major axis thereof directed to the rubbing directions with respect to the alignment films 8 and 11, and the major axis direction of the liquid crystal 4 is rotated through 90 degrees to be thereby twisted between a pair of alignment films 8 and 11.
In the liquid crystal device 1, in which the liquid crystal 4 is twist-oriented in the foregoing manner, a phase difference of the liquid crystal is different depending on viewing angles. Therefore, as described below, a contrast characteristic exhibits anisotropy (direction of anisotropy is different if the liquid crystal 4 is twisted to right or twisted to left) in response to the orientation state of the liquid crystal 4 (major axis direction and tilt of major axis) disposed between the substrates 2 and 3. In FIG. 2, a point O denotes a point on a light-emitting surface of the liquid crystal device 1, ON denotes a normal vertically extending from the point O on the light-emitting surface, OP denotes a direction of light emitting from the point O, and OY denotes a direction in parallel with the light-emitting surface of the liquid crystal device 1 (reverse bright vision direction described later). Further, an angle θ denotes an angle, by which the light-emitting direction OP is tilted from the normal ON (elevation angle), an angle φ denotes an angle (azimuth angle) made by a plane PON with respect to a plane YON (plane including line segments OY and ON). As shown in FIG. 2, the rubbing direction A1 of the alignment film 8 makes the angle of 45 degrees with respect to the OY direction, and the rubbing direction A2 of the alignment film 11 makes the angle of 135 degrees with respect to the OY direction.
FIG. 3 shows a contour drawing representing a contrast ratio of light emitting from the light-emitting surface of the liquid crystal device 1 to the OP direction (θ, φ). In the drawing, the contrast ratio is increased in the center and gradually reduced toward the periphery. FIG. 3 is denoted by means of polar coordinates, in which a radial coordinate represents the elevation angle θ, and an angle coordinate thereof represents the azimuth angle φ. According to the drawing, the contrast ratio in the light-emitting surface of the liquid crystal device 1 shows the anisotropy with a small contrast in a Y direction (direction of φ=zero degree) and a large contrast in a direction reverse to the Y direction (direction of φ=180 degrees).
FIG. 4A shows a contrast characteristic in a plane vertical to a plane including the direction OY and the line segment ON and also vertical to the light-emitting surface of the liquid crystal device 1 (plane of φ=90 degrees and φ=270 degrees). FIG. 4B shows a contrast characteristic in the plane including the direction OY and the line segment ON (plane of φ=zero degree and φ=180 degrees). As shown in FIG. 4A, the contrast characteristic in the plane of φ=90 degrees and φ=270 degrees exhibits a lateral symmetry centered on the line segment ON. On the other hand, as shown in FIG. 4B, referring to the contrast characteristic in the plane of φ=zero degree and φ=180 degrees, the contrast ratio exhibits its peak at a position being tilted in the azimuth of φ=180 degrees, while the contrast ratio considerably drops when deviated from the position. Therefore, the contrast ratio remarkably decreases in the azimuth of φ=zero degree.
In the case of exhibiting such a contrast anisotropy, a φ direction, where a maximum point of the contrast ratio is disposed, is called a bright vision azimuth, while a φ direction reverse to the φ direction is called a reverse bright vision azimuth. In the present case, the Y direction constitutes the reverse bright vision azimuth. In the specification, a direction in a third-dimensional space, where light having a higher contrast ratio enters and emits with respect to the liquid crystal device is called a bright vision direction. A direction in the third-dimensional space having the same elevation angle θ as in the bright vision direction on a side, where light having a lower contrast ratio enters and emits with respect to the liquid crystal device, is called a reverse bright vision direction. The bright vision azimuth is a two-dimensional azimuth, where the light having the higher contrast ratio is emitted when viewing the liquid crystal device from the light-emitting-surface side. The reverse bright vision azimuth is a two-dimensional azimuth, where the light having the lower contrast ratio is emitted when viewing the screen from the light-emission side. The bright vision azimuth and the bright vision direction are identical to each other, and the reverse bright vision azimuth and the reverse bright vision direction are identical to each other when viewing from a direction vertical to the light-emitting surface, while they are respectively reverse to each other when viewing from the light-entering side.
The projection type image display apparatus, which is designed to send out bright parallel ray from a light source, employs a light source 21 configured in such a manner as shown in FIG. 5. The light source 21 is comprised of a lamp 22, such as a xenon lamp disposed backward, and a reflecting mirror 23 disposed behind the lamp 22 and having a shape of rotational parabolic surface, wherein light emitted from the lamp 22 is reflected by means of the reflecting mirror 23 to be thereby converted into the substantially parallel ray and emitted forward.
The light emitted from the light source 21 is similar to the parallel ray, however is actually an emission light having a light volume distribution in a donut-shape with a dark center part. Therefore, a lens optical system (not shown), which serves to illuminate the light volume distribution in a substantially uniform manner on a liquid crystal screen, is generally formed between the liquid crystal and the light source. The lens optical system serves to uniform the light volume of the light emitted from the light source on the liquid crystal surface. However, the light volume of the light entering the liquid crystal screen marks its peak in a light-entering direction α and a spread angle in the light-entering direction results in around 2α on one side (see FIG. 22A). FIG. 6 shows an angle distribution of an emitting light volume in the plane including the OY direction and the line segment ON (plane of φ=zero degree and φ=180 degrees), which shows the contrast ratio in the bright vision/reverse bright vision directions (same as in FIG. 4B) a broken line. When the elevation angle θ in the bright vision direction at a peak point therein is represented by θo, the θo is around a few degrees (<α).
As described, there is very little light vertically entering the liquid crystal device 1 from the light source 21. The light from the light source 21 enters the liquid crystal device 1 slantwise with a spread of 2·α and at a tilt of around α. Therefore, the light entering the liquid crystal device 1 from the reverse bright vision direction is blocked by the light blocking film 12 and the black matrix region 7. As a result, the contrast in the liquid crystal device 1 is relatively increased. As shown in FIG. 7, however, the light entering the liquid crystal device 1 from the bright vision direction is also blocked in part by the light blocking film 12 and the black matrix region 7 (In FIG. 7, light-blocking area is hatched). Thus, the liquid crystal device 1 configured in the manner as shown in FIG. 1 had the problem that the screen is darkened.
FIG. 8 shows a schematic illustration of a liquid crystal device 13 having a conventional configuration in a cross-section view. The liquid crystal device 13 employs a lens array substrate 14 as the counter substrate in place of the glass substrate. The lens array substrate 14 has an integral multilayer structure, in which a lens layer 15 having lens patterns and a refractivity of n1 and a flat glass 17 are attached to each other by means of an adhesive 16 having a refractivity of n2 (<n1). In a boundary between the lens layer 15 and the adhesive 16 is formed a micro lens array 18. Respective micro lenses constituting the micro lens array 18 are arrayed as opposed to the respective pixel electrodes 6 of the TFT substrate 2.
In the foregoing liquid crystal device 13, light entering from the bright vision direction is converged on the pixel electrodes 6 of the liquid crystal device 13 through the respective micro lenses as shown in FIG. 8, thereby making it difficult for the light from the bright vision direction to be blocked by the light blocking film 12 and the black matrix region 7. Light can be thus more efficiently utilized to thereby brighten a screen of the liquid crystal device 13.
The light emitted from the light source 21 is a light with a relatively small tilt and narrow spread as shown in a thick continuous line in FIG. 6. When the light from the light source passes through the micro lens array 18, an optical axis of the light is largely tiled and the spread thereof is broadened as shown in a thin continuous line in FIG. 6. In particular, light coming from the reverse bright vision direction is spread to a range of a very poor contrast. Such a light from the reverse bright vision direction is also converged on the pixel electrodes 6. As a result, the light blocking film 12 and the black matrix region 7 does not serve well to block the light, thereby creating the problem that a contrast of the liquid crystal device 13 is lowered.
In the projection type image display apparatus, an image brightness and contrast are very important factors. However, in the conventional technology, when such a liquid crystal device 1 as shown in FIG. 1 is used, the brightness is undermined, while the contrast is undermined when such a liquid crystal device 13 as shown in FIG. 8 is used. Therefore, it was difficult to obtain a liquid crystal device suitable for practical use.
According to a liquid crystal device 19 recited in No. 2001-249316 of the Publication of the Unexamined Patent Applications (cited reference 1), an optical center axis of respective micro lenses constituting a micro lens array 20 in a lens array substrate 14 is shifted in parallel with a bright vision-azimuth side with respect to a center position of pixel openings (pixel electrodes 6) in a TFT substrate 2 to thereby improve a contrast.
FIG. 9 shows a partial section of a schematic configuration of the liquid crystal device 19. In the liquid crystal device 19, a lens array substrate 14 has an integral multilayer structure, in which a lens layer 15 having lens patterns and a refractivity of n1 and a flat glass 17 are attached to each other by means of an adhesive 16 having a refractivity of n2 (>n1). In a boundary between the lens layer 15 and the adhesive 16 is formed a micro lens array 20. Further, the optical center axis of the micro lenses constituting the micro lens array 20 is shifted in parallel with the bright vision azumuth, and an edge of the respective micro lenses on the bright vision-azimuth side is formed in a plane vertical to the lens array substrate 14.
According to the liquid crystal device 19, the optical center axis of the micro lenses is shifted to the bright vision azimuth. Therefore, as shown in FIG. 9, light entering the liquid crystal device 19 from a bright vision direction transmits through the micro lenses to be thereby converged on the pixel electrodes 6 as tilted in the bright vision direction. On the contrary, light having a low contrast entering the liquid crystal device 19 from a reverse bright vision direction is refracted by the micro lenses to be thereby blocked by a blocking film 12 of a counter substrate 3 and a black matrix region 7 of a TFT substrate 2.
Therefore, according to the liquid crystal device 19, the incoming light is converged by means of the micro lens array to thereby more efficiently utilize light and realize a bright image display. Further, because such a simple configuration that the optical center axis of the micro lenses is shifted to the bright vision azimuth is employed, vertically incoming light is twisted to the bright vision direction to thereby transmit through the liquid crystal and, further, light entering from the reverse bright vision direction is blocked, thereby achieving a display having a high contrast. In other words, a liquid crystal device, in which the brightness is not really lost and a display of a good contrast characteristic is achieved, can be manufactured.
FIG. 10 shows a liquid crystal device 19 according to another embodiment, which is configured and exerts an effect in a substantially same manner as in the liquid crystal device 19 shown in FIG. 9. In the liquid crystal device 19 of FIG. 10, an edge of the respective micro lenses on the bright vision-azimuth side is rounded.
However, in the liquid crystal device 19 configured in the foregoing manner, as shown in FIG. 11, when light in the reverse bright vision direction enters a substantially vertical region disposed on the edge of the micro lens on the bright vision-azimuth side (hereinafter, referred to as non-continuous surface of micro lenses), the light transmits through the pixel electrodes 6 of the TFT substrate 2 and is emitted to the reverse bright vision direction, which lowers an image contrast. Further, as shown in FIG. 11, when light enters the non-continuous surface of the micro lenses from the bright vision direction, the light is emitted to a direction largely deviated from the opposed counter pixel electrodes 6. The light, then, enters the adjacent pixel electrodes 6 and becomes stray light, which decreases the brightness and contrast of the image. The liquid crystal device 19 of FIG. 10 having a curved part corresponding to the non-continuous surface, which is not quite an ideal shape, also undergoes the same behavior of light. As a result, it was actually difficult to improve the contrast of the liquid crystal device 19 in the case of the liquid crystal device 19 having the configuration shown in FIGS. 9 and 10.